Bulk storage tanks, particularly those that are vented to the atmosphere, tend to lose significant amounts of volatile fluid contents due to evaporative losses. Such losses, if ignored, can have an undesirable effect on the accuracy of stock reconciliation. Moreover, various countries, including the United States and Australia, levy penalties based on evaporative losses. Evaporative loss assessment is currently only calculated periodically (typically once a year for permitting purpose) using earlier obtained estimates and calculation procedures as described in standards such as EPA AP 42 and API CELE Chapter 19, for example. Improved tank monitoring including more accurate and more timely evaporative loss assessment is needed to realize improved operations (i.e., operational excellence), lower cost and losses, and for increasing awareness and reducing environmental emissions.